Transcontainers and other large bulky freight are typically loaded into and unloaded from a ship by means of an apparatus having a horizontally displaceable support, a frame having a lower end and supported for vertical movement on the support, and a grab carried on the lower end of the support. Alternately the grab can be suspended from the support by cables.
With each system the grab is dropped down onto the object being picked up, clamps or the like are engaged to lock the grab to the object, and then the grab is pulled back up. The freight is then displaced horizontally by movement of the support, which can either ride on a portal or be mounted on an arm of a crane, to a location above the drop-off location where the grab is lowered and the clamps are released.
As described in U.S. Pat. No. 1,900,867 and German 1,556,636, hooks or spreaders are used to pick up the objects being moved. Such arrangements are particularly difficult to use in that they must be positioned perfectly above the object being picked up in order to engage the grab with the object, normally fitting it to standardized fittings on the transcontainer. In addition once the object is lifted clear and it is to be moved horizontally, the object is likely to swing or sway, making it difficult to handle and normally requiring that it be moved quite slowly to minimize this problem. While it has been suggested in German 4,342,522 to provide actuators to align the grab with the object, this solution is imperfect and does nothing to prevent the load from swaying when transported horizontally.